The human lymphocyte antigen ("HLA") system is the major histocompatibility complex in man. It, therefore, constitutes the strongest barrier for tissue and organ transplants between individuals, apparently distinguishing between self and non-self. In addition, HLA factors have been demonstrated to be associated with increased susceptibility to a wide variety of diseases. Therefore, the antigens of the HLA system have found use in diagnostic typing processes and products for determining an individual's susceptibility to a wide variety of diseases and his characteristics as a donor or acceptor of a tissue or organ transplant [F. H. Bach and J. J. Van Rood, N. Engl. J. Med., 295, pp. 806-13 (1976)].
From a genetic point of view the HLA system is fairly well characterized. See e.g., L. P. Ryder et al., "Genetics of HLA Disease Association", Ann. Rev. Genet., 15 pp. 169-87 (1981); J. L. Strominger et al., in The Role of the Major Histocompatibility Complex in Immunobiology, M. Dorf, ed., Garland SPTM Press, pp. 115-172 (1981); T. Sasazuki et al., "The Association Between Genes In The Major Histocompatibility Complex and Disease Susceptibility", Ann. Rev. Med., 28, pp. 425-52 (1977). It consists of a series of more or less highly polymorphic loci situated within an interval of about 2 centimorgan (cM) on the short arm of chromosome 6. Three loci in that system (HLA-A, B and C) encode one class of codominantly expressed alloantigens (Class 1). Another locus (HLA-D/DR) encodes a second class of codominant alloantigens with a high degree of recognized polymorphism (Class 2). Three other loci, controlling some of the initial components (C2, C4 and factor Bf) of the complement cascade, also belong to the HLA system (Class 3). Finally, there is an non-specific region in the HLA complex designated Ia. Region Ia appears related to, but different than, the DR locus.
The biology of the HLA system is less well understood. Class 1 factors are distributed in all tissues except erythrocytes. Class 2 factors are substantially restricted to .beta.-lymphocytes and mononuclear phagocytic cells and the Class 3 complement factors are directly involved in the activation of the C3 factor, the key component in the complement system. The HLA-DR antigens appear to be involved in immunological phenomena--immuna responsiveness, T-cell suppression, T-cell and .beta.-cell cooperation and T-cell and macrophage presentation [B. Benacerraf in "The Role Of The Major Histocomatibility Complex In Immunobiology", M. E. Dorf, ed., Garland SPTM Press, pp. 255-69 (1981)].
The HLA-DR antigens are composed of two non-covalently-linked glycosylated peptide chains, a heavy or .alpha.-chain of about 35,000 molecular weight and a light or .beta.-chain of about 29,000 molecular weight, than span the cellular membrane [Strominger et al., supra; and Ryder et al., supra]. Intracellularly, a third peptide chain of about 32,000 molecular weight is associated with the .alpha.- and .beta.-chains [D. J. Charron and H. O. McDevitt, J. Exp. Med., 152, pp. 185-365 (1980); Strominger supra]. It appears that the light or .beta.-chain carries the polymorphism of the HLA-DR antigens, while the .alpha.-chain and third chain appear identical in different individuals [G. Corte et al., Proc. Natl. Acad. Sci. USA, 78, pp. 534-38 (1981); Charron and McDevitt, supra]. Several serologically distinct HLA-DR antigens have been identified--HLA-DR1 through HLA-DR8--and monoclonal antibodies have defined subparts of DR antigens within homozygous cell lines [V. Quaranta et al., J. Immunol., 125, pp. 1421-25 (1980 ); S. Carrel et al., Mol. Immunol., 18, pp. 403-11 (1981)]. At least two DR .beta.-chains can also be distinguished in several homozygous cell lines by peptide analysis [R. S. Accolla et al., Proc. Natl. Acad. Sci. USA, 78, pp. 4549-51 (1981)].
Several other loci also exist that encode polymorphic Ia-like antigens that are closely linked but not identical, to HLA-DR [G. Corte et al., Nature, 292, pp. 357-60 (1981); Nadler et al., Nature, 290, pp. 591-93 (1981)]. These distinct subregions are called DC [R. Tosi et al., J. Exp. Med., 148 pp. 1592-1611 (1978); D. A. Shackelford et al., Proc. Natl. Acad. Sci. USA, 78, pp. 4566-70 (1981)] and SB [S. Shaw et al., J. Exp. Med., 156, pp. 731-43 (1982)]. The DC antigens are in strong linkage disequilibrium with the DR antigens. SB antigens control a secondary lymphocyte reaction and are encoded in a region centromeric to the DR loci.
At present the HLA-DR antigens are isolated serologically by precipitation with antisera. Therefore, the exact nature of the HLA-DR determinants is uncertain. However, these antigens have found use in typing processes and products to determine the compatibility of donors and acceptors for tissue or organ transplants and to determine susceptibility of an individual to a wide variety of diseases. For example, Ryder et al., supra, has reported the following disease susceptibilities based on DR1 through DR8 typing:
__________________________________________________________________________ Positive Frequency (%) Relative Ethiological Disease Typing Patients Controls Risk Fraction .DELTA. __________________________________________________________________________ Dermatitis D/DR3 85 26.3 15.4 0.80 herpetiformis Coeliac disease D/DR3 79 26.3 10.8 0.72 D/DR7 also increased Sicca syndrome D/DR3 78 26.3 9.7 0.70 Idiopathic Addison's D/DR3 69 26.3 6.3 0.58 disease Graves' disease D/DR3 56 26.3 3.7 0.42 Insulin-dependent D/DR3 56 28.2 3.3 0.39 diabetes D/DR4 75 32.2 6.4 0.63 D/DR2 10 30.5 0.2 -- Myasthenia gravis D/DR3 50 28.2 2.5 0.30 B8 47 24.6 2.7 0.30 SLE D/DR3 70 28.2 5.8 0.58 Idiopathic membraneous D/DR3 75 20.0 12.0 0.69 nephropathy Multiple sclerosis D/DR2 59 25.8 4.1 0.45 Optic neuritis D/DR2 46 25.8 2.4 0.27 Goodpasture's syndrome D/DR2 88 32.0 15.9 0.82 Rheumatoid arthritis D/DR4 50 19.4 4.2 0.38 Pemphigus D/DR4 87 32.1 14.4 0.81 IgA nephropathy D/DR4 49 19.5 4.0 0.37 Hydralazine-induced SLE D/DR4 73 32.7 5.6 0.60 Hashimoto's thryoiditis D/DR5 19 6.9 3.2 0.13 Pernicious anemia D/DR5 25 5.8 5.4 0.20 Juvenile rheumatoid D/DR5 50 16.2 5.2 0.40 arthritis: pauciart __________________________________________________________________________
From these typings, it can be seen that an individual typed positive for D/DR4 has a 6.4 times higher risk of developing insulin-dependent diabetes than individuals typed negative for D/DR4.
In some cases it has also been demonstrated that a disease is more severe in patients having the disease-associated antigen that in those who do not have that antigen. For example, multiple sclerosis progresses more rapidly in D/DR2-positive patients than in D/DR2-negative patients. Moreover, relapses in certain diseases are more common in patients positive for the disease-associated antigens. Plainly, then, HLA-dr typing has great diagnostic and prognostic value.
However, the use of such typing processes and products and, therefore, the attainment of the important advantages that they would provide in identifying acceptable transplant donors and recipients and disease-susceptible individuals, has been severely restricted because the present typing procedure is complex and time consuming and because there are not sufficient HLA-DR antigens available to provide a useful and economical source for such processes and products.